This invention relates to an image forming apparatus such as a full-color copying machine or color printer.
Conventionally, a so-called four-series tandem type full-color copying machine having four image forming units placed side by side along a conveyor belt and used for respectively forming toner images of colors of yellow (Y), magenta (M), cyan (C), black (B) based on image signals which have been subjected to color separation is known as an image forming apparatus for outputting a color image.
The image forming unit of each color has a photosensitive drum which is rotatably set in contact with the conveyor belt, a charging device for charging the drum surface to a preset potential, an exposure device for exposing the drum surface to form an electrostatic latent image thereon, a developing device for supplying toner to the electrostatic latent image on the drum surface to develop the image, and a transfer device for transferring the developed toner image onto a sheet of recording paper attracted to and transferred by the conveyor belt. The recording paper attracted to the conveyor belt passes through the four image forming units, toner images of the respective colors are transferred onto the recording paper in a superposed form, and then the recording paper is fed to the fixing device which fixes the toner images of the respective colors on the recording paper to form a color image.
The four-series tandem type color copying machine changes the position of the conveyor belt according to the monochrome mode and color mode and prevents the color drums from being brought into contact with the conveyor belt in the monochrome mode.
The monochrome mode is a single color mode using only black and only the image forming unit for forming a toner image of black (B) is set in contact with the conveyor belt in the monochrome mode. The color mode is a multi-color mode of full color and the four image forming units for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), black (B) are set in contact with the conveyor belt in the color mode.
Conventionally, switching between the monochrome mode and color mode, that is, movement of the conveyor belt is not started until the copy button is depressed after switching between the monochrome mode button and the color mode button is made. The reason why switching between the monochrome mode button and the color mode button is not made immediately after the monochrome mode button or color mode button is depressed is to prevent switching between the monochrome mode and the color mode from frequently occurring by an erroneous operation.
The conventional method has a problem that the copy operation is not performed until the movement of the conveyor belt is terminated since the movement of the conveyor belt caused by switching between the monochrome mode and the color mode is made after the user has depressed the copy button, and therefore, the user is kept waiting.
An object of this invention is to provide a fourseries tandem type full-color copying machine in which waiting time of the user can be shortened by previously making the movement of the conveyor belt caused by specification of switching between the monochrome mode and the color mode before the copy button is depressed.
In order to attain the above object, this invention provides an image forming apparatus comprising a feeding section for feeding a recording medium by use of a conveyor belt; a plurality of image forming units placed side by side along the feeding section and having rotatable photosensitive drums, for respectively transferring images of different colors onto a recording medium fed by the feeding section; specifying means for selectively specifying a monochrome mode in which only one of the plurality of image forming units is used to transfer an image onto a recording medium fed by the feeding section and a color mode in which the plurality of image forming units are used to transfer respective images onto a recording medium fed by the feeding section; an automatic document feeder having a detector for detecting documents placed on a document tray, for sequentially feeding the documents on the document tray onto a document table; reading means for reading an image of the document fed onto the document table by the automatic document feeder; first changing means for determining that the document is placed on the document tray of the automatic document feeder based on a detection signal from the detector and changing the state of the plurality of image forming units and the conveyor belt to a state in which only one of the plurality of image forming units is set in contact with the conveyor belt by moving the image forming units or the conveyor belt when switching from the color mode to the monochrome mode is specified by the specifying means; second changing means for determining that the document is placed on the document tray of the automatic document feeder based on a detection signal from the detector and changing the state of the plurality of image forming units and the conveyor belt to a state in which all of the plurality of image forming units are set in contact with the conveyor belt by moving the image forming units or the conveyor belt when switching from the monochrome mode to the color mode is specified by the specifying means; instructing means for instructing start of an image forming process after a change is made by one of the first and second changing means; and image forming means for forming an image read by the reading means on a recording medium by use of one image forming unit which is set in contact with the conveyor belt by the first changing means or forming an image read by the reading means on a recording medium by use of all of the image forming units which are set in contact with the conveyor belt by the second changing means according to an instruction from the instructing means.
Further, this invention provides an image forming apparatus comprising a feeding section for feeding a recording medium by use of a conveyor belt; a plurality of image forming units placed side by side along the feeding section and having rotatable photosensitive drums, for respectively transferring images of different colors onto a recording medium fed by the feeding section; specifying means for selectively specifying a monochrome mode in which only one of the plurality of image forming units is used to transfer an image onto a recording medium fed by the feeding section and a color mode in which the plurality of image forming units are used to transfer respective images onto a recording medium fed by the feeding section; a document cover for covering a document placed on a document table; detecting means for detecting an open/closed state of the document cover; reading means for reading an image of a document fed onto the document table; first changing means for changing the state of the plurality of image forming units and the conveyor belt to a state in which only one of the plurality of image forming units is set in contact with the conveyor belt by moving the image forming units or the conveyor belt when switching from the color mode to the monochrome mode is specified by the specifying means and the open state of the document cover is detected by the detecting means; second changing means for changing the state of the plurality of image forming units and the conveyor belt to a state in which all of the plurality of image forming units are set in contact with the conveyor belt by moving the image forming units or the conveyor belt when switching from the monochrome mode to the color mode is specified by the specifying means and the open state of the document cover is detected by the detecting means; instructing means for instructing start of an image forming process after a change is made by one of the first and second changing means; and image forming means for forming an image read by the reading means on a recording medium by use of one of the image forming units which is set in contact with the conveyor belt by the first changing means or by use of all of the image forming units which are set in contact with the conveyor belt by the second changing means according to an instruction from the instructing means.
Further, this invention provides an image forming apparatus comprising a feeding section for feeding a recording medium by use of a conveyor belt; a plurality of image forming units placed side by side along the feeding section and having rotatable photosensitive drums, for respectively transferring images of different colors onto a recording medium fed by the feeding section; specifying means for selectively specifying a monochrome mode in which only one of the plurality of image forming units is used to transfer an image onto a recording medium fed by the feeding section and a color mode in which the plurality of image forming units are used to transfer images onto a recording medium fed by the feeding section; an automatic document feeder having a detector for detecting documents placed on a document tray, for sequentially feeding the documents on the document tray onto a document table; reading means for reading an image of a document fed onto the document table by the automatic document feeder; a moving mechanism for vertically moving the conveyor belt; first changing means for determining that the document is placed on the document tray of the automatic document feeder based on a detection signal from the detector and changing the state of the plurality of image forming units and the conveyor belt to a state in which only one of the plurality of image forming units is set in contact with the conveyor belt by downwardly moving the conveyor belt by use of the moving mechanism when switching from the color mode to the monochrome mode is specified by the specifying means; second changing means for determining that the document is placed on the document tray of the automatic document feeder based on a detection signal from the detector and changing the state of the plurality of image forming units and the conveyor belt to a state in which all of the plurality of image forming units are set in contact with the conveyor belt by upwardly moving the conveyor belt by use of the moving mechanism when switching from the monochrome mode to the color mode is specified by the specifying means; instructing means for instructing start of an image forming process after a change is made by one of the first and second changing means; and image forming means for forming an image read by the reading means on a recording medium by use of one of the image forming units which is set in contact with the conveyor belt by the first changing means or by use of all of the image forming units which are set in contact with the conveyor belt by the second changing means according to an instruction from the instructing means.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.